This invention relates generally to a method and apparatus for recording and reproducing an information signal and, more particularly, is directed to a method and apparatus for recording and reproducing a color television signal comprised of a video signal and an audio signal on a magnetic tape with a plurality of rotary magnetic heads.
Information signal recording and reproducing apparatus for recording and reproducing a video signal on a magnetic tape by means of a rotary magnetic head assembly are well known in the art. For example, in a helical scan video tape recorder (VTR), at least one rotary magnetic head is rotated at a predetermined angle with respect to the longitudinal or tape running direction of a magnetic tape as the latter is advanced so as to form successive video tracks extending obliquely on the magnetic tape. With the helical scan video tape recorder, it is possible to achieve high density recording of the video signal by advancing the magnetic tape at a slow running speed and, at the same time, providing a high relative speed between the magnetic head assembly and magnetic tape. However, with known helical scan video tape recorders in which an audio signal is recorded and reproduced on an audio track extending in the longitudinal or tape running direction of the magnetic tape by a stationary magnetic head, there results a deterioration of the signal-to-noise (S/N) ratio and an increase in the wow and flutter when the speed of advancement of the magnetic tape is reduced. This, of course, results in a deterioration in the quality of the reproduced audio signal, causing the audio signal to have unsatisfactory quality when reproduced.
In order to overcome the aforementioned problem in the recording and reproducing of an audio signal by a stationary magnetic head, it has been proposed to effect the recording and reproducing of the audio signal by means of a rotary magnetic head. With this proposal, an overscan section is provided for each oblique track, for example, by increasing the tape winding angle about the guide drum assembly of the helical scan video tape recorder. In this manner, each record track obliquely formed on the magnetic tape by the rotary magnetic head assembly includes a video track section and an audio track section, the latter of which corresponds to the aforementioned overscan section. The audio signal that is recorded and reproduced with respect to the audio track section of each track is processed as high density data obtained by processing the signal with a time axis or base compression and a time axis or base expansion.
In one known apparatus, two rotary magnetic heads are provided and are spaced apart by 180.degree.. Thus, each head scans alternate ones of the successive tracks extending obliquely on the magnetic tape. It has been proposed to digitize and compress the audio signal and record the same in an overscan section at the beginning of each track with such known apparatus. Such arrangement provides the desirable feature of recording the video signal and digitized audio signal in separate sections of each track so that editing thereof can be readily achieved. In other words, with such arrangement, it becomes relatively easy to re-record a different audio sound track in the overscan section of each track for the same video signal. However, in such case, tape jitter and the like, due to, for example, contraction and expansion of the magnetic tape and inaccuracies in the tape transport system, may result in errors in the timing between the already recorded tracks and the magnetic heads which are to re-record the audio signal therein. As a result, the re-recorded digitized audio signal will not completely overlap, and will therefore not completely erase, the digitized audio signal originally recorded in the overscan section of each track. This unerased portion of the digitized audio signal originally recorded in the record tracks, of course, results in undesirable noise during playback.
Tape jitter and the like may also result in another problem with the aforementioned helical scan video tape recorder. More particularly, because the digitized audio signal is recorded in compressed form in each track, reproduction of the digitized audio signal from each track occurs during only a fraction of the respective field interval within which the digitized audio signal is situated. During the remainder of the respective field interval, the head used for reproducing the digitized audio signal is not in contact with the magnetic tape. However, due to leakage of the video signal reproduced by the other head, undesirable noise may be leaked to an audio digital processing circuit in the reproducing section of the helical scan video tape recorder. In this regard, the audio digital processing circuit in the reproducing section is generally supplied with a window signal having a duration equal to the period of the digitized audio signal in the overscan section of each track. The window signal enables the audio digital processing circuit to expand, decode and convert the digitized audio signal to an analog audio signal only during the period of the window signal so that any extraneous or leaked noise is not reproduced. However, when tape jitter and the like occurs due to, for example, contraction and expansion of the tape and inaccuracies in the tape transport system, a portion of the digitized audio signal in the overscan section of each track may be reproduced outside of the period of the window signal, so that part of the digitized audio signal is not reproduced.